In 1992, a young man headed into the Alaskan wilderness seeking a new way of life and perhaps an escape from the modern world. Four months later, emaciated and helpless, he died. This short, fatal experiment with simple living was exhaustively explored by Jon Krakauer in his book, Into The Wild. But one core mystery remained: Was the journey a slow-motion suicide mission? Or was his death an accident? Jon Krakauer had a theory: unintentional poisoning. Now, he thinks he has proof. He tells Audie Cornish about the new evidence.

AUDIE CORNISH, HOST:

From NPR News, this is ALL THINGS CONSIDERED. I'm Audie Cornish.

Back in 1992, a young man headed into the Alaskan wilderness seeking a new way of life, perhaps an escape from the modern world. Four months later, emaciated and helpless, he died. The story of Christopher McCandless and his short, fatal experiment with simple living was exhaustively explored in a 1996 book by Jon Krakauer. It's called "Into the Wild." But one core mystery remained: Was McCandless' journey a slow-motion suicide mission, the results of recklessness or ignorance about the realities of living in the wild? Or was his death an accident?

Jon Krakauer had a theory: Unintentional poisoning. But now, Krakauer thinks he has proof. Krakauer joins us now from Boulder, Colorado. Jon, welcome to the program.

JON KRAKAUER: Thank you.

CORNISH: So a lot of what people know about Christopher McCandless came from his journal, right? He actually kept writing about his experience. And what did it tell you about how he lived and how he died?

KRAKAUER: Well, the journal is very brief and cryptic, so you have to interpret it. But he recorded all the food that he killed. He noted the plants that he ate. He recorded the weather on pieces of birch bark. So - and he also took a lot of photographs that were recovered with his body, several rolls of film. So - and his photographs show what he was eating. So things were going pretty well in July when he - early July when he returned to the bus after trying and failing to cross the river because it was so hot. So he...

CORNISH: And this is a bus that was a makeshift shelter that was just out there already.

KRAKAUER: It was out there already. It had been used for many years by hunters and trappers out at the stampede trails it's called, like a day's journey from the road. It was kind of this midway station. And he stumbled upon it by chance, and it had this wood stove in it and a bed in the back and it was - it's in a pretty place, and he thought it was a great place to make it his base camp. So that's where he lived for most of these three and a half months.

So he decided just to keep living at the bus, foraging food, killing small game. And things were going pretty well. Until the end of July, there's this ominous journal entry, July 30th. It reads: extremely weak. Fault of potato seed. Much trouble just to stand up. Starving. Great jeopardy. You know, before this entry, there's nothing to suggest he was in trouble. After that, there's other signs in his journal that, you know, he was in big trouble. And then a little over three weeks later, on August 18, he crawled in the back of the bus and died.

Well, this led me to conclude, as it would almost anybody, that the seeds had somehow laid him low, maybe killed him outright. So I sent these seeds - I collected some seeds when I visited the bus and sent these seeds to an esteemed biochemist in Fairbanks and had them tested. And the chemist - they came back and the chemist said, no, these plants aren't poisonous. He said, you know, I tore this plant apart. I'd eat it myself.

So that perplexed me. I mean, how do I reconcile what the chemist said with what McCandless' journal said? So I just kept combing the scientific literature. And by chance, I came across this essay by Ronald Hamilton.

CORNISH: And this gentleman named Ron Hamilton helps you get to the bottom of things, right, from an unlikely place, right? He looks to World War II and concentration camp victims.

KRAKAUER: Right. And it was a place no one had thought to look before or no one I knew about, and it was brilliant. I mean, he, you know, Hamilton deserves the credit for this. He's the guy that figured this out. And he was familiar with this concentration camp called Vapniarca in the Ukraine during World War II where Jews were kept. And at this concentration camp, one of the officers decided to conduct this grotesque experiment where he fed the inmates a plant called grass pea, very similar to the plant that McCandless ate, the wild potato.

He fed them this seed of the grass pea, which had been eaten for centuries and had been known to be toxic under certain conditions. It had been known since at least 400 B.C. And he wanted to, you know, he was just being sadistic and he wanted to study the symptoms. And it turns out, when people eat the grass pea, especially when they are not getting enough food otherwise and have a limited diet, they become paralyzed. Their legs become paralyzed. They become too weak to walk, much trouble just to stand up.

And Ron Hamilton, after reading "Into the Wild" had this aha moment, and he wondered if it could be the same toxic agent, ODAP. It's a neurotoxin and amino acid. And Hamilton decided to test wild potato seeds to see if they also had ODAP, this poison. So he got some seeds. He sent them to the chemistry department of the university where he worked. And they did some testing, which highly suggested that yes, these seeds did indeed contain ODAP.

So I simply took the final step, as I also last August got a hold of some wild potato seeds, and sent them to a very sophisticated lab in Ann Arbor that had state-of-the-art techniques. And sure enough, absolutely, definitely, certainly the wild potato seeds contained ODAP, this deadly neurotoxin that causes paralysis if you eat it when you're not getting enough other nutrients.

CORNISH: Jon, why was it important to you to get to the bottom of this? I mean, does it have to do with this debate about whether or not Christopher McCandless had acted recklessly? I mean, is that something you felt you needed to defend against?

KRAKAUER: Yeah, I did. I mean, I should say, right away. As I point out in the very first pages of "Into the Wild," I approached this book not as a normal, you know, unbiased journalist. I admitted that I identified with McCandless very much. When I was his age, when I was 23, a year younger - he was 24 when he died. When I was 23, I went to Alaska by myself into the glaciers of the coast range and climbed a mountain by myself. It was incredibly reckless, incredibly stupid. But I was lucky. And I survived, and I came back to tell my story.

And I was not suicidal. I was just young and suffered from the stupidity and hubris of youth. And I believe McCandless was very much, you know, the same way, that he wasn't trying to kill himself. He was trying to test himself. And he wasn't very careful about it. So it was important to me, you know, to defend McCandless against his critics, and they are a legion, who say he was suicidal or an idiot. I - and I just wanted to know. And I wrote this book and I speculated that these seeds had killed him, and everyone keeps saying, well, the seeds aren't poisonous.

And that journal entry about extremely weak, fault of potato seed kept gnawing at me, and it was important to me. It was important to me to get the book right, you know? If it hadn't - if the seeds hadn't contained ODAP, I would have put that in a new edition of the book: Well, it seems like the seeds didn't kill him, that he just starved to death out of stupidity. But I don't have to write that now. I can write the opposite.

CORNISH: Jon Krakauer, author of the book "Into the Wild." His latest article is online at the New Yorker. Jon Krakauer, thank you for speaking with me.

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